This invention pertains to an improved three-piece wound golf ball construction including a solid center core, an intermediate thread wound layer, and an outer cover piece. It pertains particularly to such a wound golf ball in which the core has larger diameter and decreased specific gravity so as to provide increased moment of inertia, spin rate and improved trajectory distance after being hit by any of various golf clubs.
Conventional known golf balls have either two-piece construction consisting of a center core and an outer core with multiple dimples provided on its outer surface, or have three-piece construction consisting of a center core, an intermediate portion which may be solid or have elastomeric thread winding, and a solid dimpled cover. The cores are usually made of natural or synthetic rubber and may be either solid or have a liquid/paste form. The cover material is usually Balata or an ionomer in combination with a suitable filler material. Variations in the chemical or physical properties of the ball materials or their physical orientation can bring about changes in the golf ball characteristics, such as feel, flight distance, rebound coefficient, durability, moment of inertia, spin etc. as has been generally described in various prior art patents.
For example, U.S. Pat. No. 4,076,255 to Moore et al discloses a three-piece golf ball having a solid core formed from a cured composition comprising polybutadiene having a high cis-content, and a monomer capable of grafting, cross-linking or chain-extending the elastomer. The core having a Shore C hardness of 60-80 is wound with a conventional elastic thread and covered with a molded cover, but the core diameter is not disclosed.
U.S. Pat. No. 4,625,964 to Yamada discloses a three-piece solid golf ball having a core formed of polybutadiene with a specific gravity of at least 1.50 and a diameter not exceeding 32 mm (1.26 inch). The ball intermediate layer has a specific gravity lower than that of the core and thickness of 3.2-5.4 mm, and the cover has a thickness of 1-3 mm and a Shore D hardness not exceeding 64.
U.S. Pat. No. 4,696,475 to Tomita et al discloses a three-piece thread-wound golf ball having improved impact resiliency and increased flight distance. The core rubber and/or the winding thread contains more than 30% by weight of an isoprene-butadiene random copolymer and has core diameter of 28-30 mm (1.10-1.18 inch).
U.S. Pat. No. 4,714,253 to Nakahara et al, discloses a three-piece solid golf ball having controlled diameters, specific gravities, and hardnesses of the central core and intermediate solid layer. The central core has a diameter of 20 to 32 mm (0.79-1.26 inch), specific gravity of 1.03 to 1.25, and a Shore C hardness of 57 to 80. The solid intermediate layer has 36-40 mm. diameter, specific gravity of 1.30-2.50 and Shore C hardness of 70-83, but it does not have a thread winding.
U.S. Pat. No. 5,397,129 to Kato el al discloses a three-piece thread-wound golf ball having a solid rubber core of 23 to 34 mm (0.91-1.34 inch) diameter. Various rubber types may be used for the core, the intermediate winding thread, and the molded cover, material including butadiene and natural rubbers.
U.S. Pat. No. 5,445,387 to Maruko et al discloses a three-piece thread-wound golf ball having a solid center of high cis-polybutadiene, a conventional thread-wound intermediate rubber layer, and a cover. The core hardness is continuously increased from its center to its outer surface. The solid core diameter is 26-31 mm (1.02-1.22 inch), the intermediate layer is 39-41 mm diameter, and ball diameter is 42.5-45 mm (1.67-1.77 inch).
Also, U.S. Pat. No. 5,553,852 to Higuchi et al discloses a three-piece solid golf ball having a center core of 29-37 mm (1.14-1.46 inch) diameter, hardness of 45-80 JlS C and a specific gravity of 1.05-1.4 but greater than that of the solid intermediate layer which has thickness of 1-3.5 mm (0.039-0.138 inch) and specific gravity of 0.9-1.2. The cover has 1-3 mm (0.039-0.118 inch) thickness and is softer than the intermediate layer.
Although golf balls having various constructions and characteristics are known, important deficiencies have been found by players to exist in these known golf ball constructions and flight characteristics. Specifically, the two-piece golf balls are far inferior in the controllability that is required when a shot is made with the middle iron or short iron clubs. In addition, a two-piece golf ball provides a poor shot feeling to the player. Known three-piece Balata golf balls exhibit spin rates that are too great for good flight distance when hit with a Driver and long iron clubs. Thus, desirable improvements in golf ball construction and spin characteristics, all achieved at reduced ball manufacturing costs, have been sought.
This invention provides an improved solid three-piece golf ball construction having a desirable combination of characteristics, and which exhibits various desirable and advantageous flight characteristics depending upon the type of golf club with which it is struck. Specifically, when the present ball is hit with a driver, other woods or longer iron club, it desirably performs much like a distance two-piece golf ball; when hit with a mid-iron club, it performs much like a two-piece Hi-spin golf ball and soft covered multi-layered ball; and when hit with a short iron or putter, the ball performs much like a three-piece liquid core Balata wound golf ball.
These desired flight characteristics for the spherical three-piece wound golf ball of this invention are achieved by providing a ball having a central solid homogeneous core which is substantially spherical and has a significantly increased diameter of 1.350-1.500 inch (34.3-38.1 mm), and preferably has 1.400-1.450 inch (35.6-36.8 mm) core diameter. The solid core is composed mainly of polybutadiene having some desirable additives, and has a specific gravity of 1.20-1.25 and a Shore D durometer hardness of 55-75, and a compression of 59-75 on a Atti compression tester. Suitable broad and preferred ranges for the chemical compositions for the golf ball core are provided in Table 1 below.
The ball core diameter is significantly larger and the core specific gravity is significantly lower than that for three-piece solid core wound golf balls which are normally available on the market at the present time. Accordingly, the ratio of the ball solid core diameter or volume to its specific gravity is significantly greater than for other known golf balls. Specifically, for the ball diameter expressed in inches, this ratio should be in a broad range of 0.9/1-1.30/1, and preferably should be 1.0/1-1.25/1. The larger solid core diameter and its lower specific gravity, in combination with the thread type for the thread-wound intermediate layer and the outer solid cover material and thickness, results in a significant desirable transfer of the ball weight and moment of inertia towards its peripheral portion. Consequently, there is a desirable increase in the total moment of inertia for the ball, which results in a corresponding increase in the initial relative spin rate of the ball after being hit with various golf clubs, as compared to other known golf balls.
According to the present invention, the ball solid central core portion having 1.35-1.50 inch (34.3-38.1 mm) diameter is thread wound to a diameter of 1.540-1.600 inch) (39.1-40.6 mm) and preferably to 1.560-1.580 inch (39.6-40.1 mm) diameter. The winding thread is a high velocity elastomeric thread material used to provide a wound intermediate portion. The thread winding material consists of blended natural and synthetic rubber having an elongation of about 800-1,000%, tensile strength of about 4,000-5,000 psi, and a rectangular cross-section dimension of 0.0625 (+/xe2x88x920.002)inches xc3x970.024 (+/xe2x88x920.006) inches. The ball cover layer or portion consists of a solid thermoplastic material having a density of 1.00-1.04 g/cm3, a flexural modulus of 5,000-10,000 psi, and a Shore D durometer hardness of 55-65. The surface of the cover portion has many small shallow dimples occupying 70-80% of the ball surface area, the dimples having a total volume of 400-500 mm3. The finished golf ball has an outer diameter of 1.680-1.688 inches (42.7-42.9 mm), a weight of 44.5-45.9 gr, a density of 1.090-1.113 g/cm3, and an Atti compression reading of 85+/xe2x88x9215 points.
One useful material blend for the golf ball cover portion contains by weight 25% +/xe2x88x925% by weight of a sodium ionomer (Dupont Surlyn 8140), 69% +/xe2x88x925% of a zinc ionomer (Dupont Surlyn 9320) and 6% of a sodium ionomer (Dupont Surly 8660) in combination with 58% titanium dioxide. Another useful blend for the ball cover contains by weight 50% +/xe2x88x925% of a sodium ionomer (Dupont Surlyn 8140), 44% +/xe2x88x925% of a zinc ionomer (Dupont Surlyn 9320), and 6% of a sodium ionomer (Dupont Surlyn 8660) in combination with 58% titanium dioxide.
This invention advantageously provides a three-piece wound golf ball having a solid center core of increased core diameter and reduced specific gravity and an elastomeric thread wound intermediate portion, which results in a desirable increased moment of inertia and spin characteristic for the ball during flight after being struck by a selected golf club. The ball thereby provides an overall desirable combination of characteristics for use under a wide range of playing conditions.
Another advantage of this invention is that three-piece golf balls are usually made with a small diameter center of only about 1.0-1.06 inch diameter, which is typically either a lively rubber ball or a liquid-filled hollow sphere. During ball manufacture, these centers must be frozen and a considerable amount of thread must be wound onto the center to bring it up to an established diameter. But for the present invention, the ball manufacturing costs are reduced by cost of the medium used to freeze the centers. Furthermore, because the center is larger in diameter, the amount and cost of the winding thread being applied to the center core and the time needed to wind it to the established size are both desirably reduced.